creatinin

Creatinine, sometimes spelled creatinin in some texts, is a waste product formed from the breakdown of creatine phosphate in muscle. It is produced at a relatively constant rate proportional to muscle mass and is mainly eliminated by the kidneys through glomerular filtration, with a smaller amount secreted by the tubules. Because its production and renal clearance are relatively stable, serum creatinine concentration is commonly used as an indirect marker of glomerular filtration rate (GFR).

Serum or plasma creatinine is used to estimate GFR, typically via formulas such as the CKD-EPI or MDRD equations. Measured creatinine clearance, using timed urine collection or, less commonly, cystatin C-based equations, can also be used. In clinical practice, a rising serum creatinine or a decreasing eGFR indicates reduced kidney function.

Creatinine measurement methods include the Jaffe reaction and enzymatic assays; enzymatic methods are more specific and less affected by interfering substances.

Normal serum creatinine values depend on age, sex, muscle mass, and laboratory reference ranges, and thus vary between individuals and laboratories.

Several factors influence creatinine levels, including age, sex, race, body size, and diet (notably meat intake). Hydration status and medications that alter kidney function or tubular secretion (for example, trimethoprim, cimetidine) can also affect levels. Acute kidney injury or chronic kidney disease typically presents with elevated serum creatinine and reduced eGFR.